1. Technical Field
The present invention relates to a paper conveying apparatus for conveying continuous paper in a printing machine for processing the continuous paper successively by from printing to machining such as punching or perforating.
2. Background Art
A printing machine for processing continuous paper successively by from printing to machining has hitherto been known which is provided with a paper feed section for feeding continuous paper, a printing section and a machining section in order in a path of continuous paper conveyance to perform printing, and machining of various sort on the way of continuous paper conveyance.
In the printing machine, it is important that a proper amount of tension be generated and imparted to continuous paper and the tension be unvaried in the printing and machining sections, to allow continuous paper to be conveyed in a stabilized state. The conventional paper conveying apparatus as disclosed in JP H10-17186 A is equipped with a first feed roll unit at an outlet side of the paper feed section, a second feed roll unit at an outlet side of the printing section and a third feed roll unit at an outlet side of the machining section, each having a feed rate (paper feed rate) set the larger the more downstream it is; for example, if the feed rate of the first feed roll unit is set at 100, the feed rate of the second feed roll unit is set at 100.01 and the feed rate of the third feed roll unit is set at 100.02, so that a proper amount of tension may be generated and imparted to continuous paper over the entire path of paper conveyance, thereby stabilizing the conveyance of paper.
To wit, due to a long path of continuous paper conveyance, a total conveyance resistance from the paper feed section to the machining section if it acts on continuous paper may break the continuous paper. To prevent this, the apparatus is so configured that with each of the first, second and third feed roll units constituted by a rotating roll and a nip roll made in pressure contact with each other, continuous paper after it is passed or fed through to each feed roll unit is caught between the rotating and nip rolls whereupon continuous paper between the first and second feed roll units has a conveyance resistance imparted thereto that is based on a difference in feed rate between them and continuous paper between the second and third feed roll units has a conveyance resistance imparted thereto that is based on a difference in feed rate between them, thereby feeding continuous paper consecutively under respective forces of conveyance of the feed roll units while preventing continuous paper from undergoing a total conveyance resistance that may be applied thereto from the paper feed section to the machining section.
In such a paper conveying apparatus of the printing machine in the prior art as mentioned above, it has been found to be still possible that with continuous paper being passed or fed through over the feed roll units when the printing machine starts to be driven (viz. in the course of initial paper threading), the continuous paper may be broken at a point on the way of conveyance.
To wit, with continuous paper from its leading end being then fed or passed successively between the rotating and nip rolls in pressure contact of the first, second and third feed roll units over the entire printing machine (all the sections therein), the tension imparted thereto is prone to be not uniform widthwise thereof (in a direction transverse to the direction of paper conveyance) at a point or points on the way of paper threading due to its meandering and such and consequently be locally larger as generated, causing continuous paper to be broken.
If continuous paper is broken on the way of a paper threading operation in the course of initial paper threading as mentioned above, the paper threading operation must be started again from the position of break, giving rise to an unscheduled operating time and thus lowering the efficiency of paper threading operation.
Especially in the case of printing and machining of continuous paper that is thin and/or has a line of perforations, the continuous paper is prone to break in the course of initial threading, making it prone to develop problems of an increased burden of operation, being time-consuming and wastefulness of paper.
In view of problems as mentioned above, it is an object of the present invention to provide a paper conveying apparatus in a printing machine, which is capable of generating a proper amount of tension and imparting it to continuous paper in the course of printing and machining, conveying continuous paper as the tension is held unvaried and stable in printing and machining sections, and preventing or restraining continuous paper from being broken in the course of initial paper threading.